1. Field of the Invention:
The present invention relates to a muffler to be connected to the exhaust outlet of an internal combustion engine for attenuating exhaust noise and vibration.
2. Description of the Relevant Art:
Conventional mufflers coupled to the exhaust outlet of internal combustion engines have a casing which defines therein an expansion or resonance chamber for dampening acoustic energy to deaden exhaust noise. Such exhaust mufflers are disclosed in Japanese Laid-Open Patent Publications Nos. 60-206921, 60-175721, and 60-206927.
The muffler with an expansion chamber disclosed in Japanese Laid-Open Patent Publication No. 60-206921 comprises an outer casing made of a molded sound-absorbing material and inner structural members such as an exhaust inlet pipe and an exhaust outlet pipe which are coupled to the outer casing, the inner structural members being unitary in structure. The outer casing defines therein an inner expansion chamber for dampening the noise of exhaust gases introduced from the exhaust manifold of the internal combustion engine. The expansion-type muffler can attenuate exhaust noise by selecting the cross-sectional area of the expansion chamber to be larger than that of the exhaust inlet pipe.
The inner expansion chamber of the expansion-type mufflers, including not only the one disclosed in the Japanese Laid-Open Patent Publication No. 60-206921 but also other expansion-type mufflers, has a volume which is usually about 5 to 6 times larger than the displacement of the internal combustion engine to which the muffler is connected. Therefore, the outer casing is large in diameter and a large space is needed to install the muffler therein. As a result, the position where the muffler is located and the positions where other accessories are disposed around the engine are subjected to limitations.
Japanese Laid-Open Patent Publication No. 59-155528 shows another muffler having an outer casing made of glass wool compressed to shape and having a hardened outer surface impregnated with heat-resistant resin. The outer casing has an expansion chamber for expanding exhaust gases to dampen exhaust noise in a low-frequency range. Exhaust noise in a high-frequency noise is absorbed and attenuated by the glass wool on the inner surface of the outer casing.
This muffler is also disadvantageous since the expansion chamber requires a large volume in order to effectively dampen the low-frequency exhaust noise.
The present invention has been made in an effort to effectively circumvent the aforesaid problems of the conventional exhaust mufflers.